Table of Contents
Week 2 [ 31 May - 6 Jun 2010 ]: Discuss TCP and memory changes, update jme driver
jme driver
- From Joshua Oreman
- jme_check_link(struct net_device *netdev, int testonly)
- In this function, I believe the code and string data used in constructing linkmsg will make it into even non-debug versions of the executable. If that's true it would be better if you could perform all the manipulations in the final DBG() line, using the ?: operator and such. It's possible the compiler is clever enough to know what strcat() does and see that linkmsg[] is not used in non-debug, though, so this may be moot.
- From Michael Brown
- if (memcmp(addr, netdev→hw_addr, ETH_ALEN))
- No need for this compare; just always write the MAC address. (This code will fail if you set the MAC to a non-default value, then try to set it back.)
- Code cleanups
- gPXE dose not use any DMA address that is above 4G
#if __x86_64__ rxdesc->desc1.flags = RXFLAG_64BIT; #endif
- Use struct ethhdr and eth_ntoa().
- Drivers should generally not try to parse the packets they transmit and receive.
- This code will break if/when software VLAN support is added.
DBG2("Received packet: " "from %02x:%02x:%02x:%02x:%02x:%02x " "to %02x:%02x:%02x:%02x:%02x:%02x " "type %04x\n", *(uint8_t *)(rxbi->data + 6), *(uint8_t *)(rxbi->data + 7), *(uint8_t *)(rxbi->data + 8), *(uint8_t *)(rxbi->data + 9), *(uint8_t *)(rxbi->data + 10), *(uint8_t *)(rxbi->data + 11), *(uint8_t *)(rxbi->data + 0), *(uint8_t *)(rxbi->data + 1), *(uint8_t *)(rxbi->data + 2), *(uint8_t *)(rxbi->data + 3), *(uint8_t *)(rxbi->data + 4), *(uint8_t *)(rxbi->data + 5), be16_to_cpu(*(uint16_t *)(rxbi->data + 12)));
- %p should be used for printing out pointer values.
DBG2("TX buffer address: %08lx(%08lx+%x)\n", (unsigned long)iob->data, mapping, len);
- This will behave poorly when memory runs out. Better is to have a refill routine that runs after the poll(), and always attempts to refill up to a specified level.
rxdesc += idx; if (jme_make_new_rx_buf(rxring->bufinf + idx)) { DBG("Dropped packet due to memory allocation error.\n"); netdev_rx_err(netdev, NULL, -ENOMEM); } else {
- From me:
- The refill function did not work correctly. Because of the error packet was reused instead of making a hole. This patch fixed it
Trace memory related codes
- Current heap size is fixed at 128K.
- Trying to figure out a way to obtain more memory, and report it to OS.
- See if it is possiable to know how much heap size we can use out of code and stack.
Schedule for memory and TCP modifications
- Trace how the gPXE boot, relocate, and fill segment informations.
- Try to understand how Michael Brown removes the even magabyte limit.
- Start a discussion on the list about how to reasonably extend gPXE's usable memory.
- Patch gPXE to support large(Several MB perhaps) heap memory.
- Design/discuss a TCP receive window advertisement algorithm.
- Patch gPXE with
TCP receive queue
,SACK Support
, andWindow scale
. - Do some benchmark against different window size, and different network environment.
- Post the result and discuss it on the gpxe mailling-list.
Some notes after trace
- Good articals for understanding Gate-A20